Conventionally, in the field of image processing, a special effect such as three-dimensional transformation, rotation, or movement is frequently applied to a source image. Moreover recently, a symmetric image point-symmetric, line-symmetric, or plane-symmetric to a main image generated by applying a special effect to a source image is obtained and it is displayed together with the main image. For example, as shown in FIG. 1, by displaying a main image 1 generated by applying three-dimensional rotational processing to the main image 1 and a symmetric image 1A line-symmetric to the main image 1, it is possible to provide an image 2 in which two persons seemingly talk to each other for audiences.
To generate the above image 2, a conventional special-effect system first obtains the main image 1 by three-dimensionally rotating a first source image by a predetermined angle and displays the image 1 at a predetermined position in the screen shown in FIG. 1. Moreover, the special effect system displays the symmetric image 1A by rotating a second source image by an angle equal to the case of the first source image in the direction opposite to the case of the first source image and thereafter, displaying the second source image at a line-symmetric position designated by an operator. Thereby, the conventional special-effect system obtains the image 2 in which the main image 1 and the symmetric image 1A are displayed at the same time.
In this case, to designate a symmetric position, the operator calculates the symmetric position of the main image 1 and inputs the position to the special effect system through an input unit such as a ten-key pad or slowly inputs positional information through an input unit such as a track ball, joy stick, or mouse to designate a symmetric position by eye measure. Therefore, the conventional special-effect system is problematic in that it takes a lot of time to designate the symmetric position thus burdening the operator. Moreover, to designate the symmetric position by an input unit such as a track ball, joy stick, or mouse, the operator designates the symmetric position by eye measure while viewing the screen in which the symmetric image 1A is displayed. Therefore, there are problems that the symmetric position cannot be accurately designated and therefore, the symmetric image 1A cannot be accurately obtained.
Furthermore, as depicted in FIG. 2, to display the main image 1 and the symmetric image 1A line-symmetric to the main image 1 and obtain an image 3 in which the symmetric image 1A is moved in accordance with the movement of the main image 1 (note the symmetrical movement of image 1A as the main image 1 moves in FIG. 2), there are problems that the symmetric position of the main image 1 must be designated each time and thereby, a lot of time is required.